The Fermi Paradox after a wave of exoplanet discoveries

In the galaxy RX J1131-1231, a team of astrophysicists from the University of Oklahoma has discovered the first known group of planets outside the Milky Way. The objects "tracked" by the gravitational microlensing technique have different masses - from lunar to Jupiter-like. Does this discovery make the Fermi paradox more paradoxical?

There are about the same number of stars in our galaxy (100-400 billion), about the same number of galaxies in the visible universe - so there is an entire galaxy for every star in our vast Milky Way. In general, for 10 years²² to 10²⁴ stars. Scientists have no consensus on how many stars are similar to our Sun (i.e. similar in size, temperature, brightness) - estimates range from 5% to 20%. Taking the first value and choosing the least number of stars (10²²), we get 500 trillion or a billion billion stars like the Sun.

According to PNAS (Proceedings of the National Academy of Sciences) studies and estimates, at least 1% of the stars in the universe revolve around a planet capable of supporting life - so we are talking about the number of 100 billion billion planets with properties similar to Earth. If we assume that after billions of years of existence, only 1% of the Earth's planets will develop life, and 1% of them will have evolutionary life in an intelligent form, this would mean that there is one billiard planet with intelligent civilizations in the visible universe.

If we only talk about our galaxy and repeat the calculations, assuming the exact number of stars in the Milky Way (100 billion), we conclude that there are probably at least a billion earth-like planets in our galaxy. and 100 XNUMX. intelligent civilizations!

Some astrophysicists put the chance of humanity becoming the first technologically advanced species at 1 in 10.²²that is, it remains insignificant. On the other hand, the universe has been around for about 13,8 billion years. Even if civilizations did not emerge in the first few billion years, there was still a long time before they did. By the way, if after the final elimination in the Milky Way there were “only” a thousand civilizations and they would have existed for about the same time as ours (so far about 10 XNUMX years), then they most likely have already disappeared, dying out or gathering others inaccessible to our level development, which will be discussed later.

Note that even “simultaneously” existing civilizations communicate with difficulty. If only for the reason that if there were only 10 thousand light years, it would take them 20 thousand light years to ask a question and then answer it. years. Looking at the history of the Earth, it cannot be ruled out that in such a period of time a civilization can arise and disappear from the surface ...

Equation only from unknowns

In trying to assess whether an alien civilization could actually exist, Frank Drake in the 60s he proposed the famous equation - a formula whose task is to "memanologically" determine the existence of intelligent races in our galaxy. Here we use a term coined many years ago by Jan Tadeusz Stanisławski, a satirist and author of radio and television "lectures" on "applied manology", because that word seems appropriate for these considerations.

According to Drake equation – N, the number of extraterrestrial civilizations with which humanity can communicate, is the product of:

R_* is the rate of star formation in our Galaxy;

f_p is the percentage of stars with planets;

n_e is the average number of planets in the habitable zone of a star, i.e., those on which life can arise;

f_l is the percentage of planets in the habitable zone on which life will arise;

f_i is the percentage of inhabited planets on which life will develop intelligence (i.e., create a civilization);

f_c - the percentage of civilizations that want to communicate with humanity;

L is the average lifetime of such civilizations.

As you can see, the equation consists of almost all unknowns. After all, we do not know either the average duration of the existence of a civilization, or the percentage of those who want to contact us. Substituting some results into the "more or less" equation, it turns out that there may be hundreds, if not thousands, of such civilizations in our galaxy.

Drake equation and its author

Rare earth and evil aliens

Even substituting conservative values ​​for the components of the Drake equation, we get potentially thousands of civilizations similar to ours or more intelligent. But if so, why don't they contact us? This so-called The paradox of Fermiego. He has many "solutions" and explanations, but with the current state of technology - and even more so half a century ago - they are all like guesswork and blind shooting.

This paradox, for example, is often explained rare earth hypothesisthat our planet is unique in every way. Pressure, temperature, distance from the Sun, axial tilt, or radiation shielding magnetic field are chosen so that life can develop and evolve for as long as possible.

Of course, we are discovering more and more exoplanets in the ecosphere that could be candidates for habitable planets. More recently, they were found near the nearest star to us - Proxima Centauri. Maybe, however, despite the similarities, the "second Earths" found around alien suns are not "exactly the same" as our planet, and only in such an adaptation can a proud technological civilization arise? Maybe. However, we know, even looking at the Earth, that life thrives under very "inappropriate" conditions.

Of course, there is a difference between managing and building the Internet and sending Tesla to Mars. The problem of uniqueness could be solved if we could find somewhere in space a planet exactly like Earth, but devoid of technological civilization.

When explaining the Fermi paradox, one sometimes speaks of the so-called bad aliens. This is understood in different ways. So these hypothetical aliens can be "angry" that someone wants to bother them, intervene and bother - so they isolate themselves, do not respond to barbs and do not want to have anything to do with anyone. There are also fantasies of "naturally evil" aliens that destroy every civilization they encounter. The very technologically advanced themselves do not want other civilizations to jump ahead and become a threat to them.

It is also worth remembering that life in space is subject to various catastrophes that we know from the history of our planet. We are talking about glaciation, violent reactions of the star, bombardment by meteors, asteroids or comets, collisions with other planets or even radiation. Even if such events do not sterilize the entire planet, they could be the end of civilization.

Also, some do not exclude that we are one of the first civilizations in the universe - if not the first - and that we have not yet evolved enough to be able to make contact with less advanced civilizations that arose later. If this were so, then the problem of finding intelligent beings in extraterrestrial space would still be insoluble. Moreover, a hypothetical “young” civilization could not be younger than us by only a few decades in order to be able to contact it remotely.

The window is also not too big in front. The technology and knowledge of a millennium-old civilization might have been as incomprehensible to us as it is today to a man from the Crusades. Far more advanced civilizations would be like our world to ants in a roadside anthill.

Speculative so-called Kardashevo scalewhose task it is to qualify the hypothetical levels of civilization according to the amount of energy they consume. According to her, we are not even a civilization yet. type I, that is, one that has mastered the ability to use the energy resources of its own planet. Civilization type II able to use all the energy surrounding the star, for example, using a structure called a "Dyson sphere". Civilization type III According to these assumptions, it captures all the energy of the galaxy. Remember, however, that this concept was created as part of an unfinished Tier I civilization, which until recently was rather erroneously portrayed as a Type II civilization seeking to build a Dyson sphere around its star (starlight anomalies). KIK 8462852).

If there was a civilization of type II, and even more so III, we would definitely see it and make contact with us - some of us think so, further arguing that since we do not see or otherwise get to know such advanced aliens, they simply do not exist. . Another school of explanation for the Fermi paradox, however, says that civilizations at these levels are invisible and unrecognizable to us - not to mention that they, according to the space zoo hypothesis, do not pay attention to such underdeveloped creatures.

After testing or before?

In addition to reasoning about highly developed civilizations, the Fermi paradox is sometimes explained by the concepts evolutionary filters in the development of civilization. According to them, there is a stage in the process of evolution that seems impossible or very unlikely for life. It is called Great filter, which is the greatest breakthrough in the history of life on the planet.

As far as our human experience is concerned, we don't know exactly if we are behind, ahead, or in the middle of a great filtration. If we managed to overcome this filter, it may have been an insurmountable barrier for most life forms in known space, and we are unique. Filtration can occur from the very beginning, for example, during the transformation of a prokaryotic cell into a complex eukaryotic cell. If this were so, life in space could even be quite ordinary, but in the form of cells without nuclei. Maybe we're just the first to go through the Great Filter? This brings us back to the problem already mentioned, namely the difficulty of communicating at a distance.

There is also an option that a breakthrough in development is still ahead of us. There was no question of any success then.

These are all highly speculative considerations. Some scientists offer more mundane explanations for the lack of alien signals. Alan Stern, chief scientist at New Horizons, says the paradox can be resolved simply. thick ice crustwhich surrounds the oceans on other celestial bodies. The researcher draws this conclusion on the basis of recent discoveries in the solar system: oceans of liquid water lie under the crusts of many moons. In some cases (Europe, Enceladus), water comes into contact with rocky soil and hydrothermal activity is recorded there. This should contribute to the emergence of life.

A thick ice crust can protect life from hostile phenomena in outer space. We are talking here, among other things, with strong stellar flares, asteroid impacts or radiation near a gas giant. On the other hand, it may represent a barrier to development that is difficult to overcome even for hypothetical intelligent life. Such aquatic civilizations may not know any space at all outside the thick ice crust. It is difficult to even dream of going beyond its limits and the aquatic environment - it would be much more difficult than for us, for whom outer space, except for the earth's atmosphere, is also not a very friendly place.

Are we looking for a life or a suitable place to live?

In any case, we earthlings must also think about what we are really looking for: life itself or a place suitable for life like ours. Assuming we don't want to fight space wars with anyone, those are two different things. Planets that are viable but do not have advanced civilizations can become areas of potential colonization. And we find more and more such promising places. We can already use observation tools to determine if a planet is in what is known as an orbit. life zone around a starwhether it is rocky and at a temperature suitable for liquid water. Soon we will be able to detect whether there really is water there, and determine the composition of the atmosphere.

The life zone around stars depending on their size and examples of Earth-like exoplanets (horizontal coordinate - distance from the star (JA); vertical coordinate - star mass (relative to the sun)).

Last year, using the ESO HARPS instrument and a number of telescopes around the world, scientists discovered the exoplanet LHS 1140b as the best-known candidate for life. It orbits the red dwarf LHS 1140, 18 light years from Earth. Astronomers estimate that the planet is at least five billion years old. They concluded that it has a diameter of almost 1,4 1140. km - which is XNUMX times the size of the Earth. Studies of the mass and density of LHS XNUMX b have concluded that it is likely a rock with a dense iron core. Sounds familiar?

A little earlier, a system of seven Earth-like planets around a star became famous. TRAPPIST-1. They are labeled "b" through "h" in order of distance from the host star. The analyzes conducted by scientists and published in the January issue of Nature Astronomy suggest that due to moderate surface temperatures, moderate tidal heating, and a sufficiently low radiation flux that does not lead to a greenhouse effect, the best candidates for habitable planets are " e” objects and “e”. It is possible that the first covers the entire water ocean.

Planets of the TRAPPIST-1 system

Thus, discovering the conditions conducive to life seems already within our reach. Remote detection of life itself, which is still relatively simple and does not emit electromagnetic waves, is a completely different story. However, scientists at the University of Washington have proposed a new method that complements the long-proposed search for large numbers. oxygen in the planet's atmosphere. The good thing about the oxygen idea is that it's hard to produce large amounts of oxygen without life, but it's unknown if all life produces oxygen.

“The biochemistry of oxygen production is complex and can be rare,” explains Joshua Crissansen-Totton of the University of Washington in the journal Science Advances. Analyzing the history of life on Earth, it was possible to identify a mixture of gases, the presence of which indicates the existence of life in the same way as oxygen. Speaking of mixture of methane and carbon dioxide, without carbon monoxide. Why no last one? The fact is that the carbon atoms in both molecules represent different degrees of oxidation. It is very difficult to obtain appropriate levels of oxidation by non-biological processes without the concomitant formation of reaction-mediated carbon monoxide. If, for example, a source of methane and CO₂ there are volcanoes in the atmosphere, they will inevitably be accompanied by carbon monoxide. Moreover, this gas is quickly and easily absorbed by microorganisms. Since it is present in the atmosphere, the existence of life should rather be ruled out.

For 2019, NASA plans to launch James Webb Space Telescopewhich will be able to more accurately study the atmospheres of these planets for the presence of heavier gases such as carbon dioxide, methane, water and oxygen.

The first exoplanet was discovered in the 90s. Since then, we have already confirmed almost 4. exoplanets in about 2800 systems, including about twenty that appear to be potentially habitable. By developing better instruments for observing these worlds, we will be able to make more informed guesses about the conditions there. And what will come of it remains to be seen.